【作者】 陈友良；

【导师】 刘家铎； 张成江；

【作者基本信息】 成都理工大学 ， 古生物学与地层学， 2008， 博士

【摘要】 本文依托中国核工业地质局重点生产中科研课题“若尔盖铀矿田富大矿体定位条件和扩大方向研究”项目的支持,在总结和深入分析前人已有大量资料的基础上,以具有代表性意义的510—1铀矿床为重点研究对象,详细研究了含矿岩系的沉积体系特征,通过对与成矿作用密切相关的热液矿物——方解石、石英、黄铁矿等矿物的微量元素、稀土元素、稳定同位素的特征进行分析和对比,查明了该区铀矿床成矿流体的来源、性质、运移演化规律和矿质沉淀富集的机理,并建立了矿床的地幔流体成矿模式,取得了以下创新性成果和认识:1、首次发现510—1铀矿床的脉石矿物（石英、方解石）具有“上酸下碱”的垂直分带规律。矿床上部（1中段）为“酸帽”,主要发育石英脉;中部（2—4中段）为“酸碱共生带”,石英脉与方解石脉均较发育;而下部（5—6中段及以下）则为“碱性基底”,主要发育方解石脉,未见石英脉。研究表明510—1铀矿床第5中段附近（距现今地表深约200m）为“酸碱分离”的地球化学界面,亦是铀发生突发成矿作用产生高度富集的部位。2、详细研究了若尔盖铀矿田含矿岩系的宏观产状和显微岩石学特征,认为该铀矿田的含矿地层岩石类型主要有硅质岩、灰岩、板岩三个大类。三类岩石的宏观和微观特征表明若尔盖铀成矿区下志留统沉积环境为陆棚环境,海平面的升降使成矿区沉积环境在内陆棚—外陆棚之间变换。在剖面结构上,表现为砂质板岩—粉砂质板岩—泥板岩（泥晶灰岩）—页岩—硅质岩的韵律叠置,这种机械物理性质迥异的多种岩石组合正是形成碳硅泥岩型铀矿极为有利的岩石组合,其实质是为铀的成矿提供了十分有利的地质环境和赋存空间。3、研究了与成矿作用密切相关的热液矿物——方解石、石英、黄铁矿的微量元素和稀土元素的地球化学特征,结果表明方解石、石英、黄铁矿具有相似的微量元素组成特征,相对富含Sr、Zr、Ba、Zn、U、Ni、Cr等元素,由矿床浅部向深部,总体上方解石微量元素的含量明显增加,其中第5中段界面附近为多种微量元素的富集地带,与矿床“酸碱分离”的界面一致,反映该界面为一重要的流体成矿地球化学界面。相关性分析表明成矿元素U与Zr、Ta、Co、Ni等深源元素呈显著的正相关,暗示成矿流体来源于深部。方解石、石英的稀土元素组成特征和配分模式均说明成矿流体主要来源于地幔,其中δCe、δEu值对氧化还原环境具有指示性意义。4、采用新的方法和现代成矿理论,对所获得的C、S、H、O稳定同位素资料进行了全面和系统的总结,按照不同成矿阶段、不同成因类型的分类原则进行了深入探讨,结果表明成矿流体来源于深部岩浆或地幔,但在成矿晚期有大气降水的加入。5、初步探讨了地幔流体与铀成矿作用的关系,认为矿化剂∑CO₂和热源来源于地幔,是地壳拉张和深大断裂活动导致部分熔融地幔上涌,与下地壳产生壳幔混熔作用,在混熔过程中提供热量和向地壳“去气”释放∑CO₂;U主要来源于壳幔混熔形成的壳幔混合流体和流体上升途经的围岩;H₂O主要来源于地幔流体、地幔流体上升途经的围岩,在成矿晚期有部分来源于大气降水。富∑CO₂、富U的成矿热液上升到压力突然降低的部位,产生减压沸腾而突发沉淀形成铀矿床,并掘此建立了矿床的地幔流体成矿模式。上述成果和认识突破了中国碳硅泥岩型铀矿成矿的传统理论,对若尔盖地区今后的找矿和预测工作具有十分重要的指导意义,同时对中国其它地区碳硅泥岩型铀矿的找矿和勘查工作亦具有新的启迪作用。更多还原

【Abstract】 This dissertation was funded by key production research projects of China Nuclear Industry Geological Survey,which named "The Study on Locating Conditions and Expanding Direction of Rich and Giant Ore Body in Zoige Uranium Ore Field" Regarding the typical 510-1 uranium deposit as research subject,the author studied detailedly the sedimentary system characteristics of ore-bearing rock series basing on summarizing and deeply analyzing of abundant references from previous researchers. Through the analysis and comparison of trace elements,rare earth elements and isotopes of hydrothermal minerals such as calcite,quartz and pyrite which are intensely related with mineralization,the sources,nature,the transportation and evolution of ore-forming fluid in uranium deposit were explored,and the mechanism of mineral deposition and enrichment was found out.The author also set up a mantle fluid ore-forming model of ore deposit.The innovative achievements and views are as follows:1.The author found for the first time that the vertical zoning of gangue minerals （quartz and calcite）in 510-1 uranium ore deposit showed an "acid top and alkaline bottom" rule.Quartz veins were developed on the top of ore deposit（level No.1）,both of quartz veins and calcite veins were developed in the mid（level No.2 to No.4）,while on the bottom of ore deposit（level No.5 to No.6 and below）,only calcite veins were developed but no quartz veins were found.The research indicated that there existed an "acid and alkali isolation" geochemical interface nearby No.5 level of 510-1 uranium deposit（200m or so below present earth surface）,which is also a high concentration position for uranium outburst of mineralization.2.Studying detailedly the macroscopic occurrence and microscopic petrology characteristics of the ore-bearing rock series in Zoige uranium ore field,the author considered that in this ore field,the ore-bearing strata rock types can be divided into three major species such as silicalite,limestone and slate.The macroscopic and microscopic characteristics of the three kinds rocks indicate that the sedimentary environment of Lower Silurian in Zoige uranium ore field is continental shelf,with alternation of the inner and outer continental shelf resulted from the growing and falling of sea level in the study area.The section structure shows a rhythm overlap of sandy slate-silty slate-argillite （micrite）-shale-silicalite.This combination of various rocks with marked difference in mechanism physical nature is a specially favorable combination for the formation of carbonaceous-siliceous-argillitic rock type uranium deposit,which is the most significant on providing quite favorable geologic environment and existence space for uranium mineralization.3.The author studied the geochemical characteristics of trace elements and rare earth elements of hydrothermal minerals such as calcite,quartz and pyrite which are intensely related with mineralization,the results showed that calcite,quartz and pyrite possess similar trace elements composing,they concentrated comparatively elements such as Sr, Zr,Ba,Zn,U,Ni,and Cr.From superficial to deep of ore deposit,the content of trace elements in calcite increased significantly.There existed a multi trace elements concentration belt nearby No.5 level interface consistent with "acid and alkali isolation" interface of ore deposit,which showed it is an important fluid ore-forming geochemical interface.Correlation analysis manifested there existing obviously positive correlation between ore-formation element U and deep-source elements like Zr,Ta,Co and Ni,which implied the deep-source ore-formation fluid.The composing and distribution patterns of rare earth elements in calcite and quartz showed the ore-forming fluid mostly came from mantle,furthermore,the values ofδCe andδEu can be used in the indication the change of oxidation and reducing environment.4.The author applying new way and present ore-forming theory,baseing on entire and systematic summarizing for stable isotopes of C,S,H and O,discussed thoroughly according different ore-forming phases and classification rule of different genetic types. The results reflected that ore-forming fluid came from deep magma or from mantle,while atmospheric water entered in late ore-forming period.5.The relationship between mantle fluid and U ore-forming was studied preliminarily,according to the results,the author considered theΣCO₂ of mineralizer and heat source came from mantle,which is because upwelling mantle forced by crustal extention and deep-seated faulting produced melt blending with lower crust,during this process,mantle provided the heat and releaseΣCO₂ to crust through outgassing.U mainly came from mantle-curst fluid formed by mantle-curst melt blending and the wall rock during fluid uplift.H₂O mainly generated from mantle fluid and the wall rock during mantle fluid uplift,and partly from atmospheric water in the late period of ore-forming. When ore-forming hydrothermal fluid concentrated withΣCO₂ and U moved up to the positon of pressure descended suddenly,outburst deposition of forming Uranium deposit occurred under decompressing boiling.According this,mantle fluid ore-forming model of ore deposit was founded.These achievements and views the author obtained brokethrough inland traditional theory on ore-forming of carbonaceous-siliceous-argillitic rock type uranium deposit, they possess extremely important directing significance for ore exploration and prediction in Zoige region from now on,meanwhile,they have new edification on exploration and survey in other inland carbonaceous-siliceous-argillitic rock type uranium deposit.更多还原